Underwater explosives as well as construction and demolition work, in general, produce sound or shock waves that travel in all directions from the site of activity at a rate of approximately four times the speed it would travel in air. Water is also non-compressible, whereas air is compressible. Thus, water more effectively transmits the energy of the sound or shock wave to the surrounding environments. As a result, underwater explosions or construction or demolition work quite often lead to severe injury or death of large numbers of marine life as a result of the crushing effect the sound or shock waves have on internal air cavities of the marine life. Generally speaking, regulatory agencies require some means for minimizing the impact of sound generated by underwater detonations or construction or demolition work.
One approach that has been utilized previously involves the provision of an air curtain, which is simply the result of releasing compressed air below the water surface such that the rising air bubbles form a semi-continuous perimeter about the site of work. The presence of the air bubbles about the perimeter have the effect of dispersing the sound or shock waves produced by the worksite, thereby absorbing the intensity of the sound or shock wave and allowing the transmission of, hopefully, only non-lethal sound or shock waves whose intensity is greatly dissipated as compared to the initial sound or shock waves emanating from the site of work. One problem with this approach is that the air curtain is often dispersed by water flow such as from tidal currents, thereby decreasing its efficacy. Depending on how great the air curtain becomes dispersed, it may have little or no effect.
Other approaches have been described in U.S. Pat. No. 6,485,229 to Gunderson et al. and U.S. Pat. No. 6,567,341 to Dreyer et al. Both of these patents describe a larger boom system that is designed to be installed in a body of water so that the boom system surrounds a site of underwater construction or demolition. Both utilize a boom curtain that includes at least two sheets of fabric material, and a gas injection system that introduces pressurized gas through an outlet positioned between the sheets of fabric material. While these systems have proven effective in attenuating sound or shock waves, due to their size the systems require time consuming set up and significant expense in materials and fabrication.
It would be desirable, therefore, to develop a device that overcomes the above-noted deficiencies of prior art sound/shock-wave attenuation systems.
The present invention is intended to overcome these and other deficiencies in the art.